CAPEC-76: Manipulating Web Input to File System Calls
Attack Pattern ID: 76
An attacker manipulates inputs to the target software which the target software passes to file system calls in the OS. The goal is to gain access to, and perhaps modify, areas of the file system that the target software did not intend to be accessible.
Likelihood Of Attack
The table below shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
Fingerprinting of the operating system: In order to create a valid file injection, the attacker needs to know what the underlying OS is.
Port mapping. Identify ports that the system is listening on, and attempt to identify inputs and protocol types on those ports.
TCP/IP Fingerprinting. The attacker uses various software to make connections or partial connections and observe idiosyncratic responses from the operating system. Using those responses, he attempts to guess the actual operating system.
Induce errors to find informative error messages
Survey the Application to Identify User-controllable Inputs: The attacker surveys the target application to identify all user-controllable inputs, possibly as a valid and authenticated user
Spider web sites for all available links, entry points to the web site.
Manually explore application and inventory all application inputs
Vary inputs, looking for malicious results: Depending on whether the application being exploited is a remote or local one the attacker crafts the appropriate malicious input containing the path of the targeted file or other file system control syntax to be passed to the application
Inject context-appropriate malicious file path using web test frameworks (proxies, TamperData, custom programs, etc.) or simple HTTP requests
Inject context-appropriate malicious file system control syntax
Manipulate files accessible by the application: The attacker may steal information or directly manipulate files (delete, copy, flush, etc.)
The attacker injects context-appropriate malicious file path to access the content of the targeted file.
The attacker injects context-appropriate malicious file system control syntax to access the content of the targeted file.
The attacker injects context-appropriate malicious file path to cause the application to create, delete a targeted file.
The attacker injects context-appropriate malicious file system control syntax to cause the application to create, delete a targeted file.
The attacker injects context-appropriate malicious file path in order to manipulate the meta-data of the targeted file.
The attacker injects context-appropriate malicious file system control syntax in order to manipulate the meta-data of the targeted file.
Program must allow for user controlled variables to be applied directly to the filesystem
To identify file system entry point and execute against an over-privileged system interface
The table below specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Design: Enforce principle of least privilege.
Design: Ensure all input is validated, and does not contain file system commands
Design: Run server interfaces with a non-root account and/or utilize chroot jails or other configuration techniques to constrain privileges even if attacker gains some limited access to commands.
Design: For interactive user applications, consider if direct file system interface is necessary, instead consider having the application proxy communication.
Implementation: Perform testing such as pen-testing and vulnerability scanning to identify directories, programs, and interfaces that grant direct access to executables.
The attacker uses relative path traversal to access files in the application. This is an example of accessing user's password file.
However, the target application employs regular expressions to make sure no relative path sequences are being passed through the application to the web page. The application would replace all matches from this regex with the empty string.
Then an attacker creates special payloads to bypass this filter:
When the application gets this input string, it will be the desired vector by the attacker.
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.